Volcanoes: Where and Why?

Name: Date: Period: Volcanoes: Where and Why?

Introduction: Geologist group volcanoes by the different kinds of rocks they produce. Some ways in which volcanic rocks differ are in color, texture (size of crystals), mineral composition and chemical composition. Let’s look at volcanoes and their rocks in one of these ways.

Objectives: After you have completed these activities, you should be able to;

1. Demonstrate one way in which volcanoes differ, and use this difference to classify them into certain groups.

2. Explain how groups of volcanoes are different.

3. Show on a map where different groups of volcanoes of different groups are located.

Procedures:

PART A: Where are most volcanoes located?

Materials: Black Pencils

1. Write down all the names of volcanoes that you know of in and around the Pacific Ocean.

2. Compare the list you made with some of your classmates.

3. Table 1: list the locations of 30 volcanoes. You are others in your class may have named some of these. Plot the location of all the volcanoes in table 1 on the map provided in the Worksheet. (Use latitude and longitude to locate these volcanoes on the map) Write the name of the volcano next to each location.

4. Where are most of these volcanoes located?

TABLE 1

Locations of Volcanoes (approximate location) Latitude Longitude Western United States: Pacific Border Lassen, California 40°N 121°W Crater Lake, Oregon 43°N 122°W Mt. Rainier, Washington 47°N 122°W Mt. Baker, Washington 49°N 122°W Craters of the Moon, Idaho 43°N 114°W Yellow Stone N.P, 44°N 110°W San Francisco Peaks, Flagstaff - Arizona 35°N 112°W Central America and West Indies Paricutin, Mexico 19°N 102°W Pop`ocatepetl, Mexico 19°N 98°W Mt. Pelee Martinique 15°N 61°W Santa Maria, Guatemala 15°N 92°W Mt. Misery, St. Kitts 17°N 63°W South America Cotopaxi, Equator 1°S 78°W Misti, Peru 16°S 71°W Alaska and Aleutian Islands Katmai, Alaska 58°N 155°W Adak, Aleutians 52°N 177°W Umnak Island, Aleutians 53°N 169°W Kamchatka, Russia (USSR) 57°N 160°E Japan Fuji, Honshu 35°N 139°E Izu-Hakone, Honshu 35°N 139°E East Indies Mayon, Philippines 13°N 124°E Krakatoa, (between Java and Sumatra) 6°S 105°E Karkar, New Guinea 5°S 146°E Central Pacific Mauna Loa or Kilauea, Hawaii 19°N 156°W Galápagos’ Islands 1°S 91°W Mariana Islands 16°N 145°E South Pacific White Island, New Zealand 37°S 177°E Auckland, New Zealand 38°S 176°E Tahiti 18°S 149°W Samoa 13°S 172°W

5. Look at the map of crustal plates in Figure 1. Where are most of the volcanoes located?

6. How might you explain their location?

PART B: What makes volcanic rock different from each other?

Materials: Three colored pencils (red, black, and blue)

1. List all the ways that you think volcanic rocks can be different from each other.

2. Compare your list to one other student. Construct an answer to the following question based upon your list and your comparison to another student.

Which characteristic of a volcano is dependent on where the rocks come from more than how the rock material erupted? Remember that when a volcano erupts the rock material may be thrown out or poured out onto the surface.

3. Listed below is the complete chemical analysis (by percent) of two volcanic rocks from two different volcanoes. Look at the information and tell which of the two chemical compounds differ by the largest amount. Which of the two chemical compounds differ by the largest amount?

When the chemical composition of many volcanic rocks is studies it is found that silicon dioxide (SiO) varies the most. The minerals in the rock and many other characteristics about the volcanic rock can be related to the silicon content. For these reasons, one simple classification system of volcanic rocks is based on whether the rock has high, medium or low silicon content.

This classification system is given below. Examples are listed in parentheses.

High Silicon Content More than 66% SiO (rhyolite, obsidian, pumice) Medium Silicon Between 66% and 52% SiO (andesite) Content Low Silicon Less than 52% SiO (basalt) Content 4. Table 2 gives the chemical composition for the volcanoes listed in Table 1. On the worksheet mark the volcanoes you plotted with a small square colored to show if it has a high, medium or low silicon content. So that you can compare your map to other students use these colors:

RED High SiO2 More than 66% BLUE Medium SiO2 Between 66% and 52% BLACK Low SiO2 Less than 52%

After coloring all your locations answer the following questions:

A. Where are most of the red squares (high SiO2) located?

B. Where are most of the blue squares (medium SiO2) located?

C. Where are most of the black squares (low SiO2) located?

5. Geologists have found that “low SiO2” rocks underlie most of the oceans, and that most of the continents are made of high SiO2. Why do you think that the different kinds of volcanoes are located where they are? List the reasons for your answer: (Hint- think about what happens at subduction zones.)

SUMMARY QUESTIONS: Please use complete sentences.

1. Based upon what you have learned in this activity how do you think volcanic rock differ in chemical composition?

2. How is the chemical composition of volcanic rock related to their location on crustal plates?

Table 1

Figure 1